The present invention generally relates to erasing of an information signal recorded on an optical disk, and in particular to a control circuit for controlling the erasing of the video signal recorded on an optical disc so that a desired video signal recorded on a specified track portion of the optical disk is selectively erased.
Optical disks are commonly used as a recording medium having a high recording density and a large capacity. Such an optical disk has an advantage in that the access time for accessing a desired information is significantly less as compared to the case when using a magnetic tape.
One typical example of the use of the optical disk is the recording of numerous still pictures for the purpose of filing. In such an application, there is a case in which a user wishes to record new information by erasing the prerecorded information already recorded on the optical disk. When a rewritable optical disk is used, such erasing is achieved relatively simply. There is another type of optical disk called a write-once type disk in which the information signal can be recorded only once. No rewriting of the information signal is possible in such a disk. Such an optical disk is used commonly. In using the write-once type optical disk, there also is a case that a particular picture should be erased so that the picture is no longer reproduced. In such a case, the information signal on a track portion of the optical disk should be erased without deteriorating other recorded signals.
When selectively erasing an information signal prerecorded on a particular portion of the track of the write once type optical disk, firstly the track portion on which the information signal to be erased is recorded is searched. The track portion is then irradiated with an optical beam which destroys the surface of the optical disk and the recorded information is erased. However, such a procedure significantly reduces the reflectivity of the surface of the optical disk in the vicinity of the track along which the surface of the optical disk is destroyed. This results in an instability in the tracking servo control or focusing servo control of the reproducing system when an information signal recorded on a track locating in a vicinity of the erased track is reproduced. Further, a so called jumping of the optical probe, which is a quick movement across the track of an optical probe produced by a reproducing head for reproduction of the recorded signal, becomes unstable when the jumping is made across the erased track which is not recorded with information signal.
Such an unstable jumping of the optical probe can be improved when an optical disk as disclosed in the commonly owned U.S. patent application Ser. No. 917,188 is used in which the assignee of the present application is the assignee. In such an optical disk, a series of address signals are recorded at the time of manufacturing of the optical disk along a row of pits forming a guide track, and the erasing of the information signal is performed so that the address signals recorded on the guide track are not erased. However, even in use of such an optical disk, the waveform of the reproduced address signal reproduced from the guide track portion adjacent to the erased track portion is modified as a result of erasing. Thus, there tends to be a problem of unstable operation when accessing prerecorded track portion in the optical disk in which some of the informations is erased.